This invention relates to wireless communications systems, such as a cellular mobile telecommunication system, that utilizes variable speech coders and, in particular, to a system for increasing the call capacity of CDMA channels that functions to determine the rate of call blockage and adjusts the transmission rate of the associated speech coders in existing wireless call connections to reduce the rate of call blockage and maintain quality of service in the cellular mobile telecommunication system.
It is a problem in the field of wireless communications systems reduce the rate of call blockage. With the explosive growth of service provided by Code Division Multiple Access (CDMA) systems, it is imperative that the available radio frequency (RF) spectrum be utilized in as efficient means as possible. CDMA technology is based upon presently available spread spectrum technology and is being adapted to support new services, such as third generation wireless communication. In a CDMA system, when the RF capacity is reached (as measured by the number of calls being supported) the service provider may be forced to add additional RF spectrum to service additional calls, if any additional RF spectrum is available. Moreover, the call traffic is controlled by an underlying stochastic process, and thus the call carrying capacity experiences peaks in usage. It is therefore desirable to have a mechanism that improves the call carrying capacity of existing RF spectrum, especially during times of peak usage.
One approach to decreasing interference within a cellular communication system is discussed in U.S. Pat. No. 5,734,967, issued to Kotzin et al., which uses the measured distance between the mobile subscriber unit and the serving base station to determine if the speech coder transmission rate should be reduced in order to reduce the associated interference level within the wireless system. This approach to controlling interference is restricted to using the measured distance criterion. It does not approach the problem from a total system point of view and does not provide a flexible means for a system provider to manage the call capacity of a wireless system.
Therefore, there is presently no system that can simply and effectively improve the call carrying capacity of existing RF spectrum in a CDMA system, especially during times of peak usage.
The above problem is solved and a technical advance achieved in the field of wireless communications systems by the present system for increasing the call capacity of CDMA channels. In this system, if call blocking is detected in the wireless communications system it may be acceptable to degrade voice quality of the communications connections within a predetermined limit in order to increase the efficiency of the available RF spectrum as measured by the call carrying capacity of this allocated RF spectrum. This is accomplished by adjusting the transmission rate of the speech coder at the mobile subscriber unit and/or the speech coder that may be located at the mobile switching center so that the call carrying capacity of the wireless communications system is therefore increased. Additionally, the situation of call blocking is monitored to determine if frame error rate targets should be adjusted to further increase the call capacity. At times when the wireless system is not experiencing peak usage, the voice quality is restored to normal levels.
The term xe2x80x9cmobile subscriber unitxe2x80x9d does not imply that the mobile unit is restricted to a moving vehicle. The present state of the art includes the use of mobile subscriber units in fixed wireless applications as an alternative to traditional wire telephony services.
The system for increasing the call capacity of CDMA channels has separate criteria and control for the reverse link and for the forward link of the CDMA channels. Separate control is desirable since the call carrying capacity may be different for the two directions and channel usage may be asymmetric. The later observation may result from data services that are offered in parallel with voice services. Data services often have the characteristic of being asymmetric, such as a file being downloaded into a personal computer. Criteria include, but are not limited to: total power, frame error rate and quality of service (QoS) associated with specific mobile subscriber units. Each mobile subscriber unit may be associated with an individual level of quality of service. For example, a wireless communication system may offer both xe2x80x9cpremiumxe2x80x9d service and xe2x80x9cbasicxe2x80x9d service, with xe2x80x9cpremiumxe2x80x9d service providing better perceived voice quality to the mobile subscriber unit under peak call durations. The number of levels of QoS is not limited to two.
This system for increasing the call capacity of CDMA channels also offers the flexibility in that various degrees of speech coder rate reduction are supported to better match the varying conditions of traffic demands and the desired quality of service. Moreover, additional flexibility is provided in that the service provider can affect only calls that are being set up or all calls (calls being set up as well as calls after set up).